1. Field of the Invention
This invention relates to the field of lubricants and process fluids. More specifically, it relates to lubricants and process fluids, based on esters of fatty acid oils, that may be designed to have pour points below −15° C. and even below −35° C. and are therefore suitable for use at such low temperatures.
2. Background of the Art
The lubricants (engine and non-engine) and process fluids industries today are searching for materials that are biodegradable. Biodegradability means that the lubricants and process fluids (hereinafter “fluids”) degrade over a period of time, which may be measured by tests such as those promulgated by the Organization of Economic Co-Operation and Development (OECD), including OECD 301B and OECD 301F. Recently, interest has been increasing in fluids which are not only biodegradable, but also renewable. Renewable products contain, by definition, high levels of renewable carbons, and standards are being set to encourage increasingly greater levels of renewability. For example, the European Ecolabel now requires that hydraulic fluids must contain at least 50 percent by weight renewable carbons.
Researchers have attempted to meet requirements or recommendations for both biodegradability and renewability by including in their fluids formulations a variety of types of natural oils. Of particular use have been the natural esters, including for example canola oil, sunflower oil, rapeseed oil, and palm oil, which have renewable carbon levels of 100 percent. Unfortunately, these natural esters often suffer from poor performance at low temperatures. This is exhibited by their having relatively high pour points, which is the highest temperature at which the material stops flowing, and is often the result of a marked viscosity increase caused by crystallization. Because natural esters typically have pour points ranging from 0 to −15 degrees Celsius (° C.), these materials may be essentially useless for the many applications where they would be exposed to these, and even lower, temperatures. Another problem with the natural esters is that they tend to have commercially undesirable levels of thermo-oxidative stability, which is due to the unsaturation within the acid fraction of their chemical structures.
In some cases synthetic esters may be used as alternatives to natural esters. Synthetic esters may, in some instances, have very low pour points (less than −50° C.) and commercially desirable levels of thermo-oxidative stability. However, most synthetic esters are derived from petrochemical feed stocks and therefore have very low (less than 50 percent by weight), and even zero, renewable carbon levels. They also are much more expensive than natural esters, and therefore may not be economically desirable for many applications.
Despite these challenges, however, there continue to be major incentives to produce fluids with commercially desirable levels of biodegradability and renewable carbons as well as very low pour points, that is, below −15° C. and particularly below −35° C. Recently Caterpillar, Inc., the world's largest manufacturer of construction and mining equipment, diesel and natural gas engines, and industrial gas turbines, released a specification, “Cat BF-2,” for bio-hydraulic fluids. This specification requires that qualifying fluids have pour points below −35° C., and also requires that such fluids meet the requirements of the European Ecolabel and therefore contain at least 50 percent by weight renewable carbons. Fluids manufacturers may be unable to meet specifications of this nature unless new fluid formulations are developed. In view of this trend, those skilled in the art must continue to seek fluid formulations that provide desirable levels of biodegradability and renewability, while also offering low pour points to enable use at cold temperatures, and relatively low cost to ensure economic and/or commercial viability.